THE PALEONTOLOGICAL DATA 109 



either in Polioptemis or in Stenodictya whether the third and fourth anal 



veins are simple principal veins or are merely branches of a principal vein. 



We are forced to conclude from this examination of the paleontological 



data that so far as the anal area is concerned the study of the ontogeny of 



Fig. no. — Polioptenns elegans (After Handlirsch). 



li\dng insects is the surest guide to a knowledge of the primitive venation of 

 this area; and that there is no reason now evident for modifying the con- 

 clusions regarding this area expressed in the diagram by Comstock and 

 Needham of the hypothetical primitive wing- venation. 



While the paleontological evidence throws little light on the venation 

 of the anal area, we can draw some conclusions from it as to the fonn of this 

 area as a whole in primitive insects. In the Pateodictyoptera the anal area 

 is not greatly enlarged; it is never separated from the preanal area by an 

 anal fuiTow; and it was never developed into a fan-like fomi, there being 

 no longitudinal folds in it. 



Summary. — A study of the paleontological data confirms to a remark- 

 able degree the conclusions drawn from the study of the ontogeny of living 

 insects as to the probable primitive type of wing-venation. 



It is evident that in the wings of the primitive insects the branches of 

 the principal longitudinal veins bore near the margin of the wing a variable 

 number of accessory veins; but it is equally evident that the number and 

 position of these accessor}' veins was not at all constant, they being of the 

 type defined in the preceding chapter as marginal accessory veins and not 

 definitive accessory veins. It is obvious, therefore, that it would be 

 impractical to introduce accessory veins into our dagram of the hypothet- 

 ical type, for the doing of this would indicate a definiteness in number and 

 position that did not exist. 



If the diagram of the hypothetical primitive type be regarded as repre- 

 senting only the principal veins and the chief branches of them, there is no 

 change that it is certain should be made in it. The only vein regarding the 

 primitive form of which there is doubt is the subcosta. This was not 

 branched in any of the known Palacodictyoptera ; but it was branched in 

 very ancient insects, that existed at the same time as the Palseodictyoptera. 



